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Background: This article explains some simple experiments that can be used in undergraduate or graduate physics or biomedical engineering laboratory classes to learn how birdcage volume radiofrequency (RF) coils and magnetic resonance imaging (MRI) work. For a clear picture, and to do any quantitative MRI analysis, acquiring images with a high signal-to-noise ratio (SNR) is required. With a given MRI system at a given field strength, the only means to change the SNR using hardware is to change the RF coil used to collect the image. RF coils can be designed in many different ways including birdcage volume RF coil designs. The choice of RF coil to give the best SNR for any MRI study is based on the sample being imaged. Results: The data collected in the simple experiments show that the SNR varies as inverse diameter for the birdcage volume RF coils used in these experiments. The experiments were easily performed by a high school student, an undergraduate student, and a graduate student, in less than 3 h, the time typically allotted for a university laboratory course. Conclusions: The article describes experiments that students in undergraduate or graduate laboratories can perform to observe how birdcage volume RF coils influence MRI measurements. It is designed for students interested in pursuing careers in the imaging field.

Dcp.pnr.trl7c.tit of'Physic..s, Urlivc,:\ity c?/ Torotrto, Tororlro. Orrr.. Cnritrdtr, M5S /A7 Rcccivcd September 8. 198 1 Thc standard Fricdn~ann-Robcrtson-Walker (FRW) big-bang modcl of thc univcrsc rcquircs spccial initial conditions: thc carly univcrsc is highly hornogcneous and isotropic cvcn though thcrc cxist causally disconncctcd regions (horizon problcm). A plane symmetric (anisotropic) solution of a systcm of field cquations in a gcncralizeci thcoly of gravitation, predicts thc beginning of thc univcrsc as a vacuum instability at a spccific fundamental timc (which can bc associated with thc Planck timc (t,)), after which matter is crcatcd as the univcrse bcgins to expand. At a time I = t, thcrc is a singular expansion, thc anisotropy vanishcs, and the physical horizon bcconlcs infinite. Thcrcafter thc solution of the field cquations gocs ovcr into thc F R W model. Thus the special initial conditions of thc FRW modcl at thc big-bang singularity t = t, arc prcdictcd by the thcory.LC modtlc big-bang standard Fricdrnan-Robcrtson-Walkcr (FRW) de I'univers rcquicrt dcs conditions initialcs spCcialcs: I'univcrs i son debut cst fortenlent homogene ct isotropc. n1i.m~ s'il conticnt dcs r6gions non rcli6cs causalcment (problemc d'horizon). Unc solution sy~nktriquc plane (anisotropc) d'un systcmc d'6quations de champ, dans une thCoric gCnkralis6e de la gravitation, pr6dit pour Ic commencement dc I'univcrs unc instabilitk du vide i un temps fondamcntal spkcifique (qui pcut Etrc associk avcc lc tc~nps dc Planck (t,,)), aprks quoi la maticre cst crC6c en mEmc temps quc I'univcrs commence son cxpansion. Pour un temps t = I,, il y a unc singularit6 diuns l'cxpansion. I'anisotropic disparait, ct I'horizon physiquc dcvient infini. Par la suite, la solution dcs equations du champ sc confond avcc Ic modelc FRW. La thCoric sc trouve donc h predirc lcs conditions initialcs sptcialcs du modclc FRW pour unc singularit6 dc big-bang i t = t c .[Tracluit par Ic journal] Can. J . Phys.. 60. 650 (1082)